When a vertebra is damaged or diseased, surgery may be used to replace the vertebra or a portion thereof with a prosthetic device to restore spinal column support. For example, vertebral body replacement is commonly required in the treatment of vertebral fracture, tumor, or infection.
In recent years, several artificial materials and implants have been developed to replace the vertebral body, such as, for example, titanium cages, ceramic, ceramic/glass, plastic or PEEK, and carbon fiber spacers. Recently, various expandable prosthetics or expandable cages have been developed and used for vertebral body replacement. The expandable prosthetic devices are generally adjustable to the size of the cavity created by a corpectomy procedure and typically are at least partially hollow to accommodate bone cement or bone fragments to facilitate fusion in vivo. Some expandable prosthesis may be adjusted prior to insertion into the cavity, while others may be adjusted in situ. One advantage of the vertebral body replacement using an expandable prosthetic device that is adjustable in situ is that it is easy to place or insert because it permits an optimal, tight fit and correction of the deformity by in vivo expansion of the device. Some other advantages offered by an expandable prosthetic device are that they can facilitate distraction across the resected vertebral defect for correction of the deformity, and allow immediate load bearing after corpectomy.
Instrumentation and specialized tools for insertion of a vertebral implant is one important design parameter to consider when designing a vertebral prosthesis. Spinal surgery procedures can present several challenges because of the small clearances around the prosthetic when it is being inserted into position. Another important design consideration includes the ability of the device to accommodate various surgical approaches for insertion of the vertebral implant.